The invention relates to a method and a device for the thermal treatment of corrosive gases.
In particular, the invention relates to chemical reactors which comprise a reactor chamber in which the reaction gases are heated to a reaction temperature by means of heating elements or groups of heating elements, the heating elements being heated by direct current flow.
To this end, the heating elements are made of an electrically conductive material and are connected to a current supply.
DE 3024320 A1 discloses a device for the high-temperature treatment of silicon compounds in the vapor phase, consisting of a thermally insulated housing having gas inlet and gas outlet openings as well as inert resistance heaters, which are arranged between these openings and are heated by direct current flow. The heating of the electrically conductive resistor bodies is preferably carried out using a star circuit in a symmetrical polyphase AC system. The individual heater groups can in this case be regulated differently to one another, i.e. heated differently by electrical current flow.
The conversion of silicon tetrachloride with hydrogen into trichlorosilane is usually carried out in a reactor at high temperatures, at least 300° C., ideally at least 850° C., and at a pressure of 0-50 bar gauge, ideally 14-21 bar gauge.
As explained in DE 3024320 A1, these reactors are often heated by electrical heating elements made of graphite, CFC, silicon carbide or similar materials.
To this end, electrical current is fed directly through the electrically conductive heating elements and the electrical energy is converted into heat in the heating element by the electrical resistance.
According to DE 3024320 A1, heat exchangers are also used inside the reactor pressure containment. The heat exchanger unit may for example consist of a set of electrically unheated graphite tubes, which are used as gas discharge, around which fresh gas flows externally according to the counterflow principle.
DE 10 2005 005 044 A1 discloses a method for converting silicon tetrachloride into trichlorosilane, in which the cooling rate of the process gas is controlled in the heat exchanger. Materials such as silicon carbide, silicon nitride, quartz glass, graphite, or graphite coated with silicon carbide, are preferably used for the heat exchangers.
Other gas deviator elements, for example cylindrical deviator apparatus, may furthermore be present inside the reactor.
On grounds of chemical stability, these installed reactor components usually consist of carbon-containing materials such as graphite, silicon carbide, CFC and all other carbon-containing refractory materials and composite materials.
DE 10 2010 029 496 A1 discloses a method for supplying energy to a load in a deposition process, in which at least a first and a second electrical quantity are provided by means of a first and a second controllable electrical switching means, the electrical quantities differing in their magnitudes and the first or second electrical quantity being switchable alternately to the load, characterized in that the energy supply is carried out in cycles having a predetermined duration T0, each cycle comprising a set number n of full oscillations of the fundamental frequency f of the supply voltages, and in that the first electrical quantity is switched through for the energy supply of the load for a first fraction n1 and the second electrical quantity is switched through for the energy supply of the load for a second fraction n2.
FIG. 1 shows a conventional device for supplying current to the heating elements, as is also described in R. Jäger “Leistungselektronik. Grundlagen and Anwendungen” [Basics and Applications of Power Electronics] (VDE-Verlag GmbH Berlin, 2nd Edition, ISBN: 3-8007-1114-1).